Compact, high intensity arc lamp with internal magnetic field producing means

ABSTRACT

A significant increase in brightness of the arc and a more focusable light-emitting region are provided in compact arc lamps by causing magnetic lines of force to diverge from the cathode tip from magnetic field producing means disposed within the cathode structure.

D United States Patent 1 1 [111 3,881,132

Miller 51 A r. 29, 1975 1 1 COMPACT, HIGH INTENSITY ARC LAMP [56]References Cited WITH INTERNAL MAGNETIC FIELD UNITED STATES PATENTSPRODUCING MEANS 3,082,307 3/1963 Greenwood et a1. 313 153 x 75 Inventor;Chm-ks Miller, Los Angeles 3,113,234 12/1963 Sch1ege1... 313/155 Calif:3,311,769 3/1967 Schmidtlem 313/184 X 3,378,713 4/1968 Ludwig 313/32[73] Assignee: California Institute of Technology, 3,384,772 5/1968Rabinowitz.... 313/155 X Pasadena, (julifi 3,408,526 10/1968 Elcnga eta1. 313/161 X [22] Filed: 1973 Prinmry E.\'aminerPa1mer C. Demeo [2!] Al, No; 385,059 Alrorney, Agent, or Firm Lindenberg, Freilich,

Wasserman, Rosen & Fernandez Related U.S. Application Data [63]Continuation-impart of Scr. No. 173,178, Aug. 19, [57] ABSTRACT 1971'abandoned" A significant increase in brightness of the arc and a [52] US Cl 3l5/344 313/32 3H/l61 more focusable light-emitting region areprovided in 3 compact arc lamps by causing magnetic lines of force IntCl Hosb 3l/06 H05b3l/28 H65b4l/00 to diverge from the cathode tip frommagnetic field [58] Fie'ld (KSearch 313/32 153 16] producing meansdisposed within the cathode structure,

12 Claims, 5 Drawing Figures 00M186 HATER INLET COOLING IATER INLETPATENTEDAPRZSISYS SHEET 10F 2' coounc WATER mm WATER OUT 40 R U E T A wG N L o o 0 WATER OUT 50 T E L N F l G.

COMPACT, HIGH INTENSITY ARC LAMP WITH INTERNAL MAGNETIC FIELD PRODUCINGMEANS The invention described herein was made in the performance of workunder a NASA contract and is subject to the provisions of Section 305 ofthe National Aeronautics and Space Act of 1958, Public Law 85-568 (72Stat. 435; 42 USC 2457).

ORIGIN OF THE INVENTION This application is a continuation in part of anapplication, Ser. No. 173,178, filed Aug. 19, 1971, entitled MagneticImprovements For Compact Arc Lamps, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention:

The present invention relates to are lamps, and more particularly, tomagnetic improvements in high pressure, xenon, compact arc lamps.

2. Description of the Prior Art:

Light sources with a continuous luminous output, and with a spectraldistribution and brightness approaching that of the sun are needed. Oneof the best present sources of such light is a direct current electricare produced in xenon gas under pressure. However, the brightness, powerhandling capacity and useful lifetime of these lamps are not greatenough for many present needs.

Present lamps operate with an electrical cathode and anode spaced inline across a small gap. These small separations raise the maximumbrightness of the very useful light emitting volume just off the cathodetip and increase the utilizable light efficiency of the lamp. An extremeheat load is applied to the anode due to the electron and ionbombardment along the arc stream direction impinging upon the anode tip,and due to the flow of hot gas, flowing in the axial direction fromcathode to anode.

Such lamps develop a fireball about 30 mils in diameter disposed justabove the apex of the cathode. The lamps are usually mounted in acollecting reflector and are focussed with respect to location of thefireball. The are contacts the anode in a small hot spot which, whilesubstantially larger than the fireball imposes a considerable heat loadon a relatively small area of the anode. These conditions may causeerosion of the cathode tip by the fireball to a condition at whichdefocusing occurs. The mode fails under the sustained and concentratedload impinging always on the same spot.

A solar simulator lamp system has been constructed in which the lightfrom a cluster of xenon, compact arc lamps is combined via anintegrating lens system and a single piece collimator to give a largediameter beam of the intensity approaching true sunlight at earth orbitoutside the atmosphere. Additional power can be provided by increasingthe number of lamps in the cluster, resulting in an increased beamdiameter but without improving the collimation angle, increasing theintensity or improving the spectral characteristics. Unless theradiation field of the lamp is changed, improvements in any of the lastthree characteristics can only be obtained at the expense of degradingother performance characteristics.

A net improvement in performance can only come from an increasedintrinsic brightness of the emitting area of each arc. The peakbrightness volumeof each lamp comprises a cylinder approximately 2 mm indiameter by 3 mm long located just off the tip of the cathode which isthe useful input area for the solar simulator system optics. An increasein the brightness of this specified area of the arc source, even ifobtained by redistribution of the light in the remainder of the field,would be advantageous. A change in the brightness of the specified areaof the arc source, can in general, be obtained by a change in theoperating parameters of the lamp which leads to a redistribution of theenergy in the arc area. Such a gain in the brightness of the imaged areadoes not necessarily mean increased efficiency, and does not necessarilyimply increased overall luminosity.

The effect of increased power on brightness of the imaged area dependson a. number of independent factors, the most important and pertinentones being:

1. Gas composition and density;

2. Anode heat transfer;

3. Specific emission of cathode and are resistance;

4. Spatial stability of cathode spot and overall stable operation of thelamp; and

5. Gas pressure in relation to container strength.

Anode heat loading has been a limiting factor in lamp operation. In Ser.No. 888,362, filed Dec. 29, 1969, now US. Pat. No. 3,635,537 whichissued on Jan. 18, 1972, the limitations set by the power-handlingcapacity of a single anode is circumvented by arranging a plurality ofanodes working with a common cathode. By sequentially firing the anodeswith increased power and shortened duty cycle, each anode can handle itsnormal design maximum as a longtime average load. While the operation issatisfactory, multiple anode lamps require careful alignment of theelements, and eleborate cooling circuits which add considerably to thecost of manufacturing each lamp.

In Ser. No. 108,810, filed Jan. 22, 1971, by this and another inventor,the complexity of the electrostatic switching method described above iseliminated by rotating the arc in a circular path around the tip of asingle watercooled anode by means of the interaction of a radialmagnetic field with the longitudinal are current. The attachment pointthen becomes a circle coaxial with the center line, part-way up theanode structure. Ser. No. 123,289 filed Mar. 11, 1971, filed by theinventor, discloses the application of longitudinal magnetic fields inthe vicinity of the cathode tip applied from magnetic means external tothe lamp envelope to stabilize the attachment of the arc discharge tothe cathode tip in sequentially fired multiple anode lamps and toneutralize stray magnetic field produced by ferro-magnetic support forclusters of lamps. The latter applications were corrective in nature andutilized external magnetic field producing means to correct problems inalready existing and assembled lamp systems.

SUMMARY OF THE INVENTION The present invention relates to providing asignificant increase in brightness and in improving the shape of thelight emitting region of compact arc lamps. These improvements areprovided by means of structure disposed within the lamp envelope andthus, are incorporated into the lamp during manufacture.

It was discovered in the course of stabilization of the arc in themultiple anode lamps and the clusters of lamps that an unexpectedincrease in lamp fireball brightness was realized when a magnetic fieldwas provided with magnetic field lines radiating from the cathode due toa dimunition of the size of the emitting area at the tip of the cathodeand to an effective increase in the arc column resistance. The increasein the are column resistance requires an increased applied voltage tomaintain a given current in the arc and this constitutes an increasedpower into the arc resulting in greater brightness and luminous outputin the emitting area.

In the compact arc lamp of this invention magnetic field producing meansare preferably provided within the cathode structure. This causes amaximum number of magnetic field lines to radiate from the cathode tipto thereby direct a maximum number of ions to the cathode, therebyincreasing the arc column resistance and having a maximum constrictingeffect on the shape of the fireball into a longer spindle-shapedemitting area which is better suited to reflectors for lamp systemsbecause of better focusability. This also provides a greater light yieldfor a given set of are operating conditions and gas pressure.Furthermore, the internal magnetic means disposed adjacent the cathodeand below the cathode tip do not interfere with or block emission oflight from the fireball. The internally generated magnetic field alsoprovides fireball stabilization and shielding against the effects ofstray magnetic fields.

A high intensity are lamp system in accordance with the inventioncomprises a sealed envelope for containing a discharge gas at greaterthan atmospheric pressure; a cathode having a tip extending into theenvelope; an anode disposed within said envelope parallel to a linethrough the axis of said cathode and having a tip spaced an arcdischarge gap from the tip of the cathode; electric discharge meansconnected to the anode and cathode for forming an arc discharge betweensaid tips; and magnetic field means disposed within said cathode forproviding a magnetic field with lines which radiate from the cathode tipduring said are discharge.

These and many other attendant advantages of the invention will becomeapparent as the invention becomes better understood by reference to thefollowing detailed description when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view, partly in section,of an arc lamp, according to the invention including magnetic sourcemeans within the cathode for providing a magnetic field wherein amaximum number of field lines radiate from the cathode tip;

FIG. 2 is a partial view of an alternate form of internal magneticcathode structure;

FIG. 3 is a partial, sectional view of a further cathode constructionincluding an internal cooling circuit;

FIG. 4 is another partial view in section of another embodiment of acathode structure including a cooling circuit;

FIG. 5 is a partial view of yet another cathode construction inaccordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, afirst embodiment of a high intensity are lamp, according to theinvention, generally includes an envelope 10, a cathode 12 having a tip16 axially spaced a discharge gap 14 from the tip 18 of an anode 20. Theenvelope is formed of a transparent 4 material, suitably quirt z, andcontains a discharge gas 11 under pressure.

In one suitable type of lamp construction, a flange 19 is attached tothe envelope 10 adjacent each open end thereof. Lamp ends 22 and 24having a plurality of apertures adjacent the outer periphery areattached to the lamp envelope 10 by means of a plurality of bolts 26extending through the apertures and through correspondingly locatedholes in flange 19 and are secured by means of nuts 28. A circulargroove which receives an end O-ring 29 is formed on the inner surface ofeach end, 22, 24 and the grooves receive each end surface of theenvelope. When the bolts 26 and nuts 28 are secured, the O-rings 29 forma gas-tight seal between the ends 22, 24 and the envelope 10.

In another suitable type of lamp construction the 0- rings 29 may bedispensed with, and metal-glass seals are used to join end caps to theenvelope serving the same function as 22 and 24.

Obviously, only the window portion of the lamp need be transparent whilethe other portions of the envelope may be constructed of higherstructural strength material such as metal or ceramic. The lamp housingmay contain an integral, internal, pre-aligned reflector, and atransparent window portion disposed transverse to the axis of theelectrodes. The cathode may be sup ported within a narrowed neck portionwhile the anode may be supported by means of straps attached to the sidewalls of the envelope. A suitable construction for such a lamp isdisclosed in my co-pending application, Ser. No. 841,278, filed July 14,1969. The improvements cited in the present application are suitable forincorporation into such a sealed beam lamp configuration.

In the particular type of lamp shown in FIG. 1, a gas inlet tube 30penetrates through lamp end 22 into the interior 32 of the envelope. Acathode support 34 is attached to the lamp end 22. One suitablestructure for a cylindrical cathode, as illustrated, comprises a bodyportion having a central recess for receiving a permanent bar magnet 62which is embedded within the cathode. The cathode is suitablymanufactured from a high temperature metal, such as tungsten andterminates in a conical tip 64. In lamps of relatively low power, thecathode does not require cooling but in higher powered lamps, thecathodes as well as the anode requires forced liquid cooling. Forexample, a hollow cap 37 is attached to the exterior of lamp end 22 andreceives a flow of coolant liquid through the coolant inlet tube 39 anddischarges the coolant liquid via coolant outlet 40. If greater heatremoval capacity is required or desired, the cathode 12 may be hollowand water circulated through the support 34 and cathode 12. In thatcase, the magnet 62 would be disposed within the cathode structure insuch manner that internal passageways for coolant would be available.

Electrical connections to the anode 20 and cathode 12 are provided byelectrical leads 56, 58 connected to the respective lamp ends 22, 24 anda dc. source, not shown. The anode 20 may be provided with an internalcoolant passageway 38 by disposing an insert 44 within the hollow anodeto form an annular coolant passage 38 which communicates with thecoolant inlet 48 and coolant outlet 53.

Sufficient operation gas which may be any of the gases chosen from theclass comprising neon, argon, krypton, xenon or their mixtures isintroduced into the evacuated and moisture-free interior of the envelopethrough the gas inlet tube 30, which is then closed. Typical internalpressures are about 3060 psig when non-operating at ambient temperature,which increases to about 70-180 psig when inoperation.

During operation, water or other coolant fluid is circulated through thehollow electrodes. Typically, the cathode and anode are about 41 inch indiameter and are separated by a discharge gap of about V2 inch. Onapplication of a d.c. electrical power input to the anode and cathode, anegative ion or electron stream and a positive ion arc stream areestablished between the tip 18 of the anode and the tip 16 of thecathode 12. The arc contacts the anode tip 18 and a fireball 66 isdisposed above the cathode tip 16. The magnet 62 creates magnetic linesof force indicated by the dotted lines. Since the magnet 62 is placedwithin the cathode and adjacent to its very tip a maximum possiblenumber of field lines or lines of force will radiate from the cathodetip for a given magnetic field. The lines of force adjacent the tip 16of the cathode and surrounding the fireball 66 radiate from the cathodeand serves to constrict the fireball a'maximum amount in the vicinity ofthe cathode tip. However, the lines 'of force are reduced in intensitynear the anode and do not apply much force in the vicinity of the anodetip. Therefore, they would not interfere or interact with any radiallydirected magnetic field from the anode which could be present to rotatethe foot of the arc as disclosed in application, Ser. No. 108,810, filedJan. 22, 1971.

An ion produced by arc discharge, in the absence of a magnetic field,may diffuse in any direction with the effect of widening the fireball66. In the presence of the magnetic lines of force, ions are constrainedby the lines of force, do not diverge and are directed onto the cathode.This slows down ion diffusion across the magnetic field lines. Inaddition, the magnetic lines of force compress the electrons in thehottest portion of the arc, i.e., the fireball 66, into the elongatedcylindrical shape illustrated. The net result of these effects is alonger spindle-shaped and brighter emitting area which is better suitedfor focussing. A more focusable fireball in itself provides a greaterlight yield for a given set of are operating conditions and gaspressure.

However, it has also been found that there is an increase in arc columnresistance due to the shape and location of this particular magneticfield. Increased resistance requires an increased applied voltage tomaintain a given current in the arc. This constitutes increased powerinput to the arc and consequently, a higher luminosity and brightnessare obtained.

From experimental data, it has been determined that the increase inpower, which is delivered to a typical 20 kw xenon arc lamp. is about 15percent for a magnetic field having an intensity from 50 to 60 gauss. Amagnetic field of about 50 gauss is a very practical field for use incompact arc lamps and may be generated safely and economically.

Referring now to FIG. 2, a cathode 12 is illustrated which includes anelcctromagnet insert 70 capable of producing a maximum number ofmagnetic lines of force radiating from the tip 16 of the cathode 12 forthe magnetic field provided. The insert 70 comprises a rod 72, the upperend of which is provided with an electromagnetic coil 74. An electricallead 76 is connected to the coil and to a power supply, not shown.

In the variation illustratedjin 3, the cathode 12 may be cooled by meansof coolant introduced through a central coolant inlet tube 80.,Theco'olant, such as water, flows'down the annular channel 82 providedbetween the inlet tube and the wall 84 of the cathode 12. A magneticfield having the desired shape and location can be provided by formingthe inlet tube 80 of soft iron and placing a permanent ceramic annularmagnet 86 adjacent the upper end of the cathode casing 84 and bydisposing a soft iron pole piece 88 within the conical tip 16 which canbe made of tungsten.

The permanent magnet 86 may suitably be replaced with an equivalentelectromagnetic windingfln the electromagnetic embodiment illustrated inFIG. 4, the collant inlet water tube 80 is surrounded by a 'coil 90which is supported within the annular coolant return channel 82. A softiron pole piece 88 is again embedded within the conical cathode tip 16.

In the cathode embodiment illustrated in FIG. 5, a permanent magnet inthe form of an annular ceramic cylinder 92 surrounds the upper portionof the cathode just below the cathode tip 16. The magnetic field linesare concentrated by means of the soft iron pole piece 88 placedimmediately behind the cathode tip, and then the field lines are causedto diverge from the cathode tip. I

All the embodiments of cathodes have in common a magnetic structurewhich is incorporated within the lamp envelope, placed within thecathode'and with a pole adjacent the very tip of the cathode. Compactarc lamp may be manufactured incorporating these features to provide anautomatic and inherent increase in lamp fireball brightness,focusability and stability.

It is to be realized that only preferred embodiments of the inventionhave been described and that numerous substitutions, alternations andmodifications are all permissible without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:

l. A high-intensity arc lamp comprising in combination:

a sealed envelope for containing a discharge gas at greater thanatmospheric pressure;

a cathode having a tip extending into the envelope;

an anode disposed within said envelope parallel to a line through theaxis of the cathode and having a tip spaced an arc discharge gap fromthe tip of the cathode;

electric power means connected to the anode and cathode for forming anarc discharge between said tips including a highly luminous fireballdisposed above the cathode tip; and

magnetic field producing means disposed internally within said cathodeand adjacent the cathode tip for establishing a magnetic field havingthe maximum possible number of field lines radiating from said cathodetip for said magnetic field for increasing lamp brightness and forimproving the shape of said arc.

2. An arc lamp according to claim 1 in which said magnetic fieldproducing means includes a ferromagnetic pole piece axially disposedwithin the structure of the cathode tip.

3. An arc lamp according to claim 2 in which an annular, permanentmagnet is supported below the cathode tip for magnetizing the pole pieceto develop the longitudinal lines of force.

4. An arc lamp according to claim 3 in which the pole piece is formed ofsoft, magnetic iron and the annular magnet is disposed within thestructure of the cathode.

5. An arc lamp according to claim 2 in which said magnetic fieldproducing means includes an electrical winding within said cathode andmeans for energizing said winding.

6. An arc lamp according to claim 1 in which said cathode is hollow andfurther includes means for flowing coolant through the hollow cathode.

7. An arc lamp according to claim 6 wherein said hollow cathode includesa soft iron inlet tube for flowing coolant through said cathode, and

said magnetic field producing means includes an electrical winding woundaround said inlet tube, and

means for energizing said winding.

8. An arc lamp according to claim 6 wherein said hollow cathode includesa soft iron inlet tube for flowing coolant through said cathode, and

said magnetic field producing means includes an annular magnet disposedwithin the structure of said cathode and enclosing said soft iron inlettube.

9. A high-intensity arc lamp comprising in combination:

a sealed envelope for containing a discharge gas at greater thanatmospheric pressure;

a cathode having a tip extending into the envelope;

an anode disposed within said envelope parallel to a line through theaxis of the cathode and having a tip spaced an arc discharge gap fromthe tip of the cathode;

electric power means connected to the anode and cathode for forming anarc discharge between said. tips including a highly luminous fireballdisposed above the cathode tip; and

a magnet positioned within said cathode,

said cathode having a magnetic pole piece adjacent said cathode tip.

10. In an arc lamp of the type comprising a cathode having a tip and ananode spaced therefrom enclosed in a gas filled envelope which upon theapplication of voltage between anode and cathode produces a fireballadjacent the cathode, a method of increasing the lamp brightness outputand improving the shape of the light emitting region thereof comprising:

generating a magnetic field from within and adjacent the tip of thecathode of said are lamp to cause a maximum possible number of fieldlines to radiate from said cathode for said magnetic field.

11. A method as called for in claim 10 wherein said step of generating amagnetic field from within and adjacent the tip of said cathodecomprises:

placing an elongated magnet within said cathode and below the tipthereof to provide a magnetic field.

12. A method as called for in claim 10 wherein said step of generating amagnetic field from within and adjacent the tip of said cathodecomprises:

placing a soft iron pole piece within the tip of said cathode; and

placing annular magnet around the periphery of said cathode and adjacentto the tip thereof.

1. A high-intensity arc lamp comprising in combination: a sealedenvelope for containing a discharge gas at greater than atmosphericpressure; a cathode having a tip extending into the envelope; an anodedisposed within said envelope parallel to a line through the axis of thecathode and having a tip spaced an arc discharge gap from the tip of thecathode; electric power means connected to the anode and cathode forforming an arc discharge between said tips including a highly luminousfireball disposed above the cathode tip; and magnetic field producingmeans disposed internally within said cathode and adjacent the cathodetip for establishing a magnetic field having the maximum possible numberof field lines radiating from said cathode tip for said magnetic fieldfor increasing lamp brightness and for improving the shape of said arc.2. An arc lamp according to claim 1 in which said magnetic fieldproducing means includes a ferromagnetic pole piece axially disposedwithin the structure of the cathode tip.
 3. An arc lamp according toclaim 2 in which an annular, permanent magnet is supported below thecathode tip for magnetizing the pole piece to develop the longitudinallines of force.
 4. An arc lamp according to claim 3 in which the polepiece is formed of soft, magnetic iron and the annular magnet isdisposed within the structure of the cathode.
 5. An arc lamp accordingto claim 2 in which said magnetic field producing means includes anelectrical winding within said cathode and means for energizing saidwinding.
 6. An arc lamp according to claim 1 in which said cathode ishollow and further includes means for flowing coolant through the hollowcathode.
 7. An arc lamp according to claim 6 wherein said hollow cathodeincludes a soft iron inlet tube for flowing coolant through saidcathode, and said magnetic field producing means includes an electricalwinding wound around said inlet tube, and means for energizing saidwinding.
 8. An arc lamp according to claim 6 wherein said hollow cathodeincludes a soft iron inlet tube for flowing coolant through saidcathode, and said magnetic field producing means includes an annularmagnet disposed within the structure of said cathode and enclosing saidsoft iron inlet tube.
 9. A high-intensity arc lamp comprising incombination: a sealed envelope for containing a discharge gas at greaterthan atmospheric pressure; a cathode having a tip extending into theenvelope; an anode disposed within said envelope parallel to a linethrough the axis of the cathode and having a tip spaced an arc dischargegap from the tip of the cathode; electric power means connected to theanode and cathode for forming an arc discharge between said tipsincluding a highly luminous fireball disposed above the cathode tip; anda magnet positioned within said cathode, said cathode having a magneticpole piece adjacent said cathode tip.
 10. In an arc lamp of the typecomprising a cathode having a tip and an anode spaced therefrom enclosedin a gas filled envelope which upon the application of voltage betweenanode and cathode produces a fireball adjacent the cathode, a method ofincreasing the lamp brightness output and improving the shape of thelight emitting region thereof comprising: generating a magnetic fieldfrom within and adjacent the tip of the cathode of said arc lamp tocause a maximum possible number of field lines to radiate from saidcathode for said magnetic field.
 11. A method as called for in claim 10wherein said step of generating a magnetic field from within andadjacent the tip of said cathode comprises: placing an elongated magnetwithin said cathode and below the tip thereof to provide a magneticfield.
 12. A method as called for in claim 10 wherein said step ofgenerating a magnetic field from within and adjacent the tip of saidcathode comprises: placing a soft iron pole piece within the tip of saidcathode; and placing annular magnet around the periphery of said cathodeand adjacent to the tip thereof.